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sum of the first four numbers in a list [#permalink]
 04 Aug 2010, 11:03
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If the sum of the first four numbers in a list of six consecutive even numbers is 908, what is the sum of the last four numbers in the list? A. 912 B. 914 C. 916 D. 920 E. 924 I tried it, but got screwed up: let 2x be one of the numbers; list: 2x-4, 2x-2, 2x, 2x+2, 2x+4, 2x+6 sum of the first four: (2x-4) + (2x-2) + (2x) + 2x+2) --> 4x-4=908 x=228 sum of last four: 2x + (2x+2) + (2x+4) + (2x+6) = 8x+12 =8(228) + 12 =1836...... non of the answers Please what is the correct approach?
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Re: sum of the first four numbers in a list [#permalink]
04 Aug 2010, 11:31
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gmatbull wrote: If the sum of the first four numbers in a list of six consecutive even numbers is 908,
what is the sum of the last four numbers in the list?
A. 912
B. 914
C. 916
D. 920
E. 924
I tried it, but got screwed up:
let 2x be one of the numbers;
list: 2x-4, 2x-2, 2x, 2x+2, 2x+4, 2x+6
sum of the first four: (2x-4) + (2x-2) + (2x) + 2x+2)
--> 4x-4=908
x=228
sum of last four: 2x + (2x+2) + (2x+4) + (2x+6)
= 8x+12
=8(228) + 12
=1836...... non of the answers
Please what is the correct approach? Let the six consecutive even numbers be x, x+2, x+4, x+6, x+8, x+10. Given: x+(x+2)+(x+4)+(x+6)=4x+12=908. Question: (x+4)+(x+6)+(x+8)+(x+10)=4x+28=?(x+4)+(x+6)+(x+8)+(x+10)=4x+28=(4x+12)+16=908+16=924. Answer: E. The way you are doing is also valid. You've just made an error in calculations, plus no need even number to be 2x it can be just even x. But anyway your approach: Sum of the first four: (2x-4)+(2x-2)+(2x)+(2x+2)=8x-4=908; Sum of the last four: 2x+(2x+2)+(2x+4)+(2x+6)=8x+12=(8x-4)+16=908+16=924. Hope it's clear.
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Re: sum of the first four numbers in a list [#permalink]
04 Aug 2010, 12:11
oh, thanks Bunuel for the corrections. Hope you aren't tired of receiving kudos; you know, people like you have made kudos a trite, and one simply wonders what else to give. Methinks, there should be a different category of kudos for genius such as Bunuel. If I may ask, please what was you GMAT score like?
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Re: sum of the first four numbers in a list [#permalink]
07 Aug 2010, 04:44
Bunuel wrote: gmatbull wrote: If the sum of the first four numbers in a list of six consecutive even numbers is 908,
what is the sum of the last four numbers in the list?
A. 912
B. 914
C. 916
D. 920
E. 924
I tried it, but got screwed up:
let 2x be one of the numbers;
list: 2x-4, 2x-2, 2x, 2x+2, 2x+4, 2x+6
sum of the first four: (2x-4) + (2x-2) + (2x) + 2x+2)
--> 4x-4=908
x=228
sum of last four: 2x + (2x+2) + (2x+4) + (2x+6)
= 8x+12
=8(228) + 12
=1836...... non of the answers
Please what is the correct approach? Let the six consecutive even numbers be x, x+2, x+4, x+6, x+8, x+10. Given: x+(x+2)+(x+4)+(x+6)=4x+12=908. Question: (x+4)+(x+6)+(x+8)+(x+10)=4x+28=?(x+4)+(x+6)+(x+8)+(x+10)=4x+28=(4x+12)+16=908+16=924. Answer: E. Hi Bunuel i did the same way .. however kindly explain this if I solve 4x+ 12 =908 , I get x = 99 ..which is not an even number . hence I was confuded whether I missed something !! thanx
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Re: sum of the first four numbers in a list [#permalink]
07 Aug 2010, 05:04
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Re: sum of the first four numbers in a list [#permalink]
07 Aug 2010, 06:38
Bunuel wrote: gmatbull wrote: If the sum of the first four numbers in a list of six consecutive even numbers is 908,
what is the sum of the last four numbers in the list?
A. 912
B. 914
C. 916
D. 920
E. 924
I tried it, but got screwed up:
let 2x be one of the numbers;
list: 2x-4, 2x-2, 2x, 2x+2, 2x+4, 2x+6
sum of the first four: (2x-4) + (2x-2) + (2x) + 2x+2)
--> 4x-4=908
x=228
sum of last four: 2x + (2x+2) + (2x+4) + (2x+6)
= 8x+12
=8(228) + 12
=1836...... non of the answers
Please what is the correct approach? Let the six consecutive even numbers be x, x+2, x+4, x+6, x+8, x+10. Given: x+(x+2)+(x+4)+(x+6)=4x+12=908. Question: (x+4)+(x+6)+(x+8)+(x+10)=4x+28=?(x+4)+(x+6)+(x+8)+(x+10)=4x+28=(4x+12)+16=908+16=924. Answer: E. The way you are doing is also valid. You've just made an error in calculations, plus no need even number to be 2x it can be just even x. But anyway your approach: Sum of the first four: (2x-4)+(2x-2)+(2x)+(2x+2)=8x-4=908; Sum of the last four: 2x+(2x+2)+(2x+4)+(2x+6)=8x+12=(8x-4)+16=908+16=924. Hope it's clear. Well done!!!! Thx and kudos
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Re: sum of the first four numbers in a list [#permalink]
08 Aug 2010, 01:49
Bunuel wrote: gauravnagpal wrote: Hi Bunuel
i did the same way ..
however kindly explain this if I solve
4x+ 12 =908 , I get x = 99 ..which is not an even number . hence I was confuded whether I missed something !!
thanx 4x+ 12 =908 --> x=224=even. i am so sorry ...i reckon sleep of mind ...i dont know how could I write this ..thanx anyways for spending time on this
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Re: sum of the first four numbers in a list
[#permalink]
08 Aug 2010, 01:49
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